Jenny forwarded to me this story about a squirrel, Finnegan, adopted by a a pregnant Papillon who was days away from giving birth to a litter of puppies.  The squirrel was but a newborn when it was found, perhaps the unfortunate recipient of a fall from mother's nest.  Finnegan was nursed back to health, but not before being adopted by the mother-to-be dog.  There are some great pictures, so I suggest you take a quick trip over there to see them.

This story, along with a great many others, always clarifies for me the protective instincts of animals which often are seen being applied across the species boundary.  A dog adopts a squirrel, dolphins adopt the offspring of other dolphin species, a hen adopts a litter of puppies, a giant gorilla adopts a kitten, and the list goes on.  You can find many stories like this on the web.  And it's not just maternal instincts at play.  I've seen a video where a small boy falls into the gorilla enclosure at a zoo; the dominant male gorilla then protects the child, gently stroking his hair as the child lay unconscious, until rescuers arrive.

It's a fascinating phenomenon.  It also demonstrates a common genetic trait handed to all animals, much like our fight or flight response.